Aromatic carbonate resins such as polycarbonate resins are thermoplastic resinous materials possessing many excellent physical and chemical properties which render them useful in a wide range of applications. They exhibit, for example, excellent properties of toughness, impact resistance, heat resistance and dimensional stability, optical clarity or non-opaqueness, and physiological inertness. Because of their excellent property spectrum, polycarbonate resins are used in various utilities including molded and extruded articles. A particular application wherein thermoplastics have found significant use is in housings for business equipment. Such housings should generally be thin, lightweight, impact resistant, heat resistant, flame resistant and preferably have a low gloss so as to be pleasing to the eye over long periods of time. Polycarbonates have been used in numerous business equipment applications wherein relatively thick housings can be employed. However, wherein thinner housings must be employed, polycarbonates have not faired as successfully. The melt viscosities of polycarbonates are generally high, therefore making it more difficult to mold thin parts. When low viscosity, low molecular weight polycarbonates are employed, the article tends to be brittle as shown by 1/8 inch Notched Izod impact testing. Accompanying this brittleness is the difficulty in flame retarding a low viscosity polycarbonate, particularly with respect to dripping and flame in thin sections. Such polycarbonates lack melt strength at the temperatures of flame, thereby making it difficult to pass the Underwriter Laboratory flaming drip criteria to qualify as V-1 or V-0. Additionally, the polycarbonate generally has a glossy exterior upon molding. The properties required for business machine housings are also desirable for other electrical containing or enclosure device housings. Examples of such housings include letter holders/mailboxes and postal boxes.
Boutni, U.S. Pat. No. 4,767,818 issued to General Electric Company allegedly solved many of the problems of utilizing polycarbonate for business equipment housings. The solution disclosed in Boutni was to employ a low molecular weight polycarbonate with an admixture of a small percent of a random block copolymer having polycarbonate blocks and diorganosiloxane blocks or a block copolymer of a vinyl aromatic and an alkyl-diene in combination with a flame retardant combination comprising a flame retardant salt. The combination is in quantities sufficient to achieve V-0 or V-1 in a part 93 mils thick and a composition having a gloss of less than 80 as measured by a Gardner gloss meter at 60.degree. gloss. This composition was placed into the marketplace as a composition useful for molding into business equipment housings. In certain applications, these compositions developed specific problems which limited their usefulness for business equipment housings. These problems included cracking, delamination and insufficient impact resistance.
A new composition of matter has been invented which meets the requirements necessary for successful marketplace performance and overcomes the specifically named disadvantages. Additionally, it has increased melt stability which allows the omposition to be processed at higher temperatures, thereby expanding the processing window available to molders of business equipment.